The present invention generally relates to an ultra high speed circuit for use in a computer or the like. The invention particularly relates to a switching circuit such as a quantum flux parametron or the like in which no voltage is generated in an output line in the steady state, and relates to a signal transmission method in such a switching circuit.
A quantum flux parametron (hereinafter, simply referred to as a QFP circuit) which is a switching circuit using Josephson Junctions operates at an ultra high speed with a very small quantity of electric power consumption. So the QFP circuit is expected to be put into practical use in a high-performance electronic computer or the like. The configuration and operational principle of such a QFP circuit will be briefly described hereunder, although they are disclosed, for example, in JP-A-59-143427; IEEE TRANSACTION ON MAGNETICS, VOL. MAG-21, No.2, March 1985; IEEE TRANSACTION ON MAGNETICS, VOL. MAG-23, No.5, September 1987; Proc. IEDM 1987; U.S. Pat. No. 4,785,426; and the like.
FIG. 2 shows the configuration of the conventional QFP circuit. The conventional QFP circuit is provided with a superconducting loop 5 and an activation line 6, the superconducting loop 5 being constituted by Josephson junctions 1 and 2 and inductors 3 and 4. The superconducting loop 5 is connected to an input line 7 and a load inductor 8. A QFP circuit can be wired to another QFP circuit in a succeeding stage. Any succeeding QFP circuits are regarded as inductors. These inductors are collectively represented by one inductor, that is, the load inductor 8. Next, the operation of the thus configured QFP circuit will be briefly described.
First, a weak input current is made to flow in the superconducting loop 5 through the input line 7 under the condition that no activation current, for example, pulse current, is applied to the activation line 6. Then, if an activation current is applied to the activation line 6, an amplified current flows in the load inductor 8 in the positive direction (in the direction from the superconducting loop 5 toward the load inductor 8) or in the negative direction (in the direction from the load inductor 8 toward the superconducting loop 5) corresponding to the direction of the input current due to the physical characteristics of the superconducting loop 5. Here, let the current in the positive direction and the current in the negative direction correspond to logical "1" and "0" respectively. Generally, the input line 7 is connected to a plurality of input terminals. Consequently, if the input terminals are connected respectively to the outputs of QFP circuits in the preceding stage, the direction of the current flowing in the input line 7 is determined by the sum of the outputs. Therefore, it is possible to realize the function of majority logic. A switching circuit using such a QFP circuit has a feature that the quantity of power consumption is very small because no voltage is generated on an output line in the steady state.